The ATHOS (AIDS Time-oriented Health Outcome Study) Program will develop prospective, longitudinal data sets that include five to eight thousand AIDS, RC, HIV-positive, and at-risk subjects and contain clinical, laboratory, economic and life quality data. Patients are consecutively enrolled from five gay private practices and five indigent clinics through their physicians who are participating investigators. Complete patient confidentiality is maintained. The program is based upon 15 years experience with The American Rheumatism Association Medical Information System (ARAMIS), the 17-center, national arthritis data resource, the staff, quality control, outcome assessment, and follow-up protocols of that program, and upon five years of prior data collection on AIDS and at-risk subjects. Data will be developed and maintained on microprocessors in physician offices and transferred, maintaining confidentiality, to Stanford for analyses. Projected analyses include study of factors influencing transitions between clinical states, factors affecting life quality, comparison of outcomes in the private community as compared with indigent health care systems, assessment of direct and indirect costs, factors influencing costs, efficacy of treatment programs (both approved and unapproved) in the affected community, and toxicity of therapy. Careful study of management, costs and outcomes in the private sector will assist in development of recommendations for deployment of public resources. The programs addresses NCHSR AIDS priorities for studies of costs and financing, stages of illness, development of HIV information systems, and development of AIDS research methods based on chronic disease data bank systems.